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If it is a true "one wire" alternator, then the feed-back problem does not apply. Such an alternator has only one large wire connected from the large post on the alternator back to the battery. It does not have any connection at all to the P1 connector on the alternator. Side story -- GM cars back in the 1970's did have exactly the problem Jim Spencer mentioned. The alternator self-exciting diodes would feed back through the idiot light on the dash and provide enough voltage to the coil to sorta kinda generate enough spark to keep the engine running on. It didn't run well, or even diesel all the time, due to the voltage drop through the idiot light, so folks confused it with the dieseling that stems from combustion chamber deposits, high idle speeds, etc. The crude emission controls of the era had created their own issues of dieseling so it took awhile before the alternator issue was fully understood. GM itself was the original source of the "diode fix". Assuming you have a side-mount distributor (don't think they make electronic ignition for front mount), then one test is as follows: With the tractor off, ease the boot back on one end of the high voltage wire from the coil to the distributor, and ensure that the wire can be pulled off with minimal effort. Block the wheels and start the tractor in neutral.
Put on some dry leather gloves. Get off the tractor, reach over and turn off the key switch. Assuming the tractor diesels, pull off the high voltage wire with your gloved hand. Watch out for the fan belt, etc. If the dieseling immediately stops, you have some sort of feedback or ignition wiring problem. If the dieseling continues without regard to the high voltage wire, then you have garden variety dieseling caused by preignition, etc.
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